Oil recovery process

ABSTRACT

A process for recovering petroleum from a subterranean hydrocarbon containing reservoir by flooding with a surfactant wherein the adsorption of surfactant by the reservoir rock is inhibited by treating the reservoir with a water soluble, strongly basic material having an oxygenated anion prior to injecting the surfactant. Preferably, treatment is accomplished by injecting an aqueous solution of sodium hydroxide or sodium meta silicate into the reservoir in an amount sufficient to satisfy substantially all of the adsorption capacity of the reservoir matrix followed by injection of an aqueous solution of the surfactant. The aqueous solution of sodium hydroxide or sodium meta silicate and the surfactant solution can be subsequently displaced through the formation by any convenient aqueous drive fluid including water.

United States Patent [1 1 Feuerbacher et al.

OIL RECOVERY PROCESS Inventors: David George Feuerbacher, Bellaire;

Mary Kay Hrncir Smith, Austin, both of Tex.

U.S. Cl. 166/274, 166/273 Int. Cl E2lb 43/22 Field of Search 166/274,273, 270,

References Cited UNITED STATES PATENTS 12/1968 Treiber et al. 166/2732/1968 Fallgatter et al.... 166/273 l/l960 Meadors 166/274 Dec. 11, 1973Primary Examiner-Stephen J. Novosad Attorney-Thomas H. Whaley et 'al.

[57] ABSTRACT A process for recovering petroleum from a-subterraneanhydrocarbon containing reservoir by flooding with a surfactant whereinthe adsorption of surfactant by the reservoir rock is inhibited bytreating the reservoir with a water soluble, strongly basic materialhaving an oxygenated anion prior to injecting the surfactant.Preferably, treatment is accomplished by injecting an aqueous solutionof sodium hydroxide or sodium meta silicate into the reservoir in anamount sufficient to satisfy substantially all of the adsorptioncapacity of the reservoir matrix followed by injection of an aqueoussolution of the surfactant. The aqueous solution of sodium hydroxide orsodium meta silicate and the surfactant solution can be subsequentlydisplaced through the formation by any convenient aqueous drive fluidincluding water.

15 Claims, No Drawings on. RECOVERY PROCESS BACKGROUND OF THE INVENTIONThis invention relates to the recovery of petroleum from a subterraneanformation. More particularly, this invention relates to the recovery ofpetroleum from a subterranean formation by flooding the formation withwater.

Petroleum is frequently recovered from subterranean formations orreservoirs in which it has accumulated by pumping or permitting thepetroleum to flow to the surface through wells drilled into thesubterranean formations. This process is referred to as primaryrecovery. A large amount of oil, generally in the range of 65 to 90percent or more, is left in the subterranean formation at the conclusionof the primary recovery program. At the conclusion of the primaryproduction recovery program, it is common practice to resort to someform of supplemental recovery technique in order to recover additionalamounts of petroleum from the subterranean formation. These supplementaloperations are frequently referred to as secondary recovery operations,although in fact they may be primary, secondary or tertiary in sequenceof their employment.

The most widely used supplemental recovery operation involves theinjection of an extraneous fluid such as water through injection wellsdrilled into the subterranean formation, so that the injectedfluiddisplaces oil through the formation to'be produced from productionwells.

While water flooding is a useful'supplemntal recovery technique, waterhas a relatively poor displacement efficiency, largely due to the factthat waterand oil are immiscible at reservoir conditions, and the highinterfacial tension that exists between the flood water and oil. Forthis reason, a large proportion of the oil is still left unrecovered atthe conclusion of a conventional waterflood.

It has been recognized by those skilled in the art of supplementalrecovery techniques, that the inclusion of a surface active agent orsurfactant in the flood water would reduce the interfacial tensionbetween the injected fluid and the reservoir petroleum, therebypromoting displacement'of the residual oil by the water more efficientlythan is possible by using water alone. For example, U.S. Pat. No.3,468,377 discloses the use of petroleum sulfonates in waterfloodoperations, and US. Pat. No. 3,553,130 discloses the use of ethyleneoxide adducts of alkyl phenols for the same purpose. U.S. Pat. No.2,233,381 discloses the use in water flooding operations of a watersoluble, surface-active, alkaline earth-resistant polyglycol ether suchas isooctylphenyl polyglycol ether. Field operations employing suchsurface-active agents or surfactants in the injected fluid have notalways been entirely satisfactory because surfactants are adsorbed bythe formation rock to a relatively high degree, resulting in an everdeclining concentration. of surfactant with distance from the injectionpoint. In order to maintain a sufficient concentration of the surfactantat the oil/water interface, it would be necessary to use a very largeconcentration of surfactant. Since waterflood operations typicallyinvolve enormous quantities of injected fluid, running into the hundredsof millions of gallons of water, the use of surfactants in sufficientlyhigh concentrations to overcome this adsorption problem has usually notbeen economically feasible.

Another serious problem in any supplemental recovery operation in whichan extraneous fluid such as water is injected into a subterraneanpetroleum containing formation to displace the petroleum or oil to theproduction means, is premature breakthrough of the injected fluid.Premature breakthrough is the breaking through of the injected ordriving fluid at the production means before an adequate portion of theformation has been swept. This problem is the described in terms ofsweep efficiency, to distinguish from the displacement efficiencydescribed above. Displacement efficiency involves the microscopic,pore-by-pore efficiency by which water displaces oil, whereas sweepefticiency is related to the gross portions of the reservoir which areswept and unswept by "the injected fluid. A major cause of poor sweepefficiency is associated with the fact that the injected fluid generallyhas a lower viscosity than the displaced fliud or petroleum. The greaterthe difference is viscosity of injected fluid and the viscosity ofpetroleum, the more pronounced will be the tendency toward prematurebreakthrough of th injected fluid, leaving a relatively large portion ofthe formation unswept.

Polymeric organic compounds which have the effect of increasing theviscosity of the injected fluid, thereby increasing the sweep efficiencyof the supplemental recovery program, have been used in recent years.For example, US. Pat. No. 3,039,529 and US. Pat. No. 3,282,337 teach theuse of aqueous polyacrylamide solutions to increase the viscosity of theinjected fluid, thereby promoting increased sweep efficiency. US. Pat.No. 3,581,824 teaches the use of polysaccharides for the same purpose.Polymers which are useful for increasing the viscosity of the injectedfluid are effective but usually are quite expensive, and sincesubstantial quantities are required, the economics of such supplementalrecovery programs are frequently a deterrent to their more wide-spreaduse. It has been observed that the commonly used viscosity increasingpolymers are adsorbed by the formation rock, and this would tend todecrease the efficiency of the material and increase the cost of anysuch program.

The above described probems have been recognized by those skilled in theart of oil recovery. The use of certain compounds as sacrificialchemicals to pretreat the formation in order to decrease the adsorptionof subsequently injected surfactant is known. For example, US. Pat. No.3,414,054 discloses the use of aqueous solutions of pyridine, US. Pat.No. 3,469,630 teaches the use of sodium carbonate and inorganicpolyphosphates, and US. Pat. No. 3,437,141 discloses the use of solublecarbonates, inorganic polyphosphates and sodium borate in combinationwith a saline solution of a surfactant having both a high and a lowmolecular weight component followed by a saline solution of the lowmolecular weight component of the surfactant. These materials have notalways been completely satisfactory from a standpoint of performance andeconomics.

. SUMMARY OF THE INVENTION The invention provides a method forrecovering petroleum from petroleum-containing subterranean formationshaving injection means and producing means completed therein, comprisingfirst injecting through the injection means-into the subterraneanformation, a preflush solution of a sacrificial inorganic material,

namely a water soluble, strongly basic material having an oxygenatedanion in sufficient quantity to be adsorbed on the formation rock and tooccupy substantially all of the adsportion sites of the rock containedin the subterranean formation, followed by injecting a surfactantsolution through the injection means into the subterranean formation,and thereafter injecting through the injection means into thesubterranean formation, the drive fluid, which is commonly water,whereby the oil is displaced through the subterranean formations to thesurface of the earth through the production means.

DESCRIPTION OF THE SPECIFIC EMBODIMENTS In carrying out this invention,a sacrificial inorganic material is injected through an injection meanscomprising one or more injection wells, into a subterraneanpetroleum-containing formation to substantially occupy or cover allpotential adsorption sites of the rock within the subterraneanformation, thereby reducing the extent of adsorption of the moreexpensive surfactant injected there-behind.

The most important characteristics for a satisfactory sacrificialinorganic material are:

1. that the material be less expensive than the surfactant,

2. that it be adsorbed readily by the subterranean formation matrix, and

3. that the presence of such adsorbed sacrificial material retards oreliminates the subsequent adsorption of surfactant on the adsorptionsites of the formation rock.

By adsorption sites of the formation rock is meant those parts of thesurfaces of the pores of the formation rock capable of adsorbing achemical compound from a solution on contact.

The sacrificial inorganic materials do not themselves have anyappreciabel affect on the recovery efficiency of waterfloodingoperations. Additional oil can be recovered only if the sacrificialinorganic material is followed by a surfactant solution with willeffectively increase the amount of oil which is displaced from thesubterranean formation pores. Ordinarily, flooding water is injectedthrough conventional injection means and into the subterranean formationbehind the surfactant solution to displace the oil and surfactant towardthe production means, and then to the surface of the earth.

The surfactant for use in such a supplemental recovery program should beinjected into the subterranean formation ahead of the flooding water,thereby achieving the desired low interfacial tension between theinjected fluid and the displaced fluid. The surfactant may be present ina hydrocarbon solvent or in an aqueous solution, or in a combinationthereof. Any type of surfactant may be used in the practice of thisinvention, although we have found non-ionic surfactants such asethoxylated substituted phenols to be especially preferable.

The surfactant used in the experimental work described later in thisspecification is a non-ionic surfactant, namely a 9.5 mole ethyleneoxide adduct of nonyl phenol.

The amount of surfactant which must be employed in the practice of thisinvention will ordinarily vary with various reservoir parameters, butgenerally will range from 0.01 to 0.1 pore volumes of an equeoussurfactant solution having dissolved therein from 0.001 to 0.5 percentby weight of the surfactant. A small amount of the sacrificial pre-flushmaterial may also be added to the surfactant solution to aid further inpreventing the adsorption of the surfactant on the formation matrix.Sodium chloride may also be added to the surfactant solution for thesame purpose.

In carrying out this invention, a sacrificial inorganic material isinjected via suitable injection means, i.e., through one or moreinjected wells completed in the subterranean hydrocarbon formation, sothat the sacrificial inorganic material enters the formation ahead ofthe surfactant. The surfactant is then injected into the subterraneanhydrocarbon containing formation, followed by the injection of water. Byinjecting the sacrificial inorganic material in this particularsequence, the sacrificial inorganic material is adsorbed by and occupiesthe adsorption sites existing in the matrix of the formation, therebyeliminating or substantially decreasing the tendency for thesubsequently injected surfactant to be adsorbed by the formation rock.As mentioned above, the surfactant may also contain the sacrificialinorganic material, in addition to sodium chloride.

Both the sacrificial inorganic material and the surfactant may beinjected into the subterranean hydrocarbon containing formation in anaqueous solution or in a nonaqueous solution such as a hydrocarbonsolvent, depending on availability and other requirements. Economicconsiderations, however, often require that the materials be injected inaqueous solutions whenever possible.

The quantity of sacrificial inorganic material to be injected into thesubterranean hydrocarbon containing formation in advance of thesurfactant solution should be sufficient to occupy substantially all ofthe active sites of the formation matrix, in order to effect the maximumreduction in the amount of surfactant that would otherwise be adsorbedby the formation. If less than this optimum amount is used, however,there will be a corresponding reduction in the adsorption of thesurfactant from the injected solution by the formation, although theamount of reduction will not be as great as in the case where theformation is completely saturated with sacrificial inorganic material.Similarly, if more than the amount of sacrificial inorganic materialnecessary to occupy all of the active sites on the formation matrix isinjected into the subterranean hydrocarbon containing formation, noreduction in oil displacement efficiency will result. The only detrimentresulting from using excess sacrificial inorganic material would be anincrease in the cost of operating the supplemental oil recovery progran.

Ordinarily the preferred range of sacrificial inorganic material willvary with the thickness of the formation, the area of pattern to beswept, and to a degree by other formation characteristics. It isconvenient to express the quantity of sacrificial inorganic material interms of pounds of material per acre foot of formation of the particularpattern which the injected fluid is expected to sweep. Ordinarily, fromabout to about 1,000 pounds per acre foot of formation of thesacrificial inorganic material described in this specification would besufficient to prevent adsorption of surfactant from injected surfactantsolution.

We have found that water soluble, strongly basic materials having anoxygen containing anion such as soluble silicates and hydroxides,specifically sodium hydroxide and soduim meta silicate are especiallyeffective sacrificial inorganic materials for use in the above describedapplication. By strongly basic material it is meant that a one molaraqueous solution of these materials have a pH of or more. Thesacrificial inorganic materials are most conveniently injected in theform of an aqueous solution, and we have found that approximately 1molar solutions of these compounds is an optimum concentration to use.The concentration may be varied, however, since it is the total amountof additive which is injected that determines the effectiveness inpreventing the adsorption of the subsequently injected surfactant. Inthe instance of using a 4 percent by weight solution of sodiumhydroxide, from about 0.005 to about 0.1 pore volumes of solution shouldbe injected into the formation prior to the injection of surfactant.Similarly, from about 0.005 to about 0.1 pore volumes of 12 percent byweight sodium meta silicate solution should be used. Since theadsorptivity of reservoirs varies considerably depending on the type offormation and the type and amount of clays that may be present in theformation, some knowledge of the formation may be necessary in order todetermine the optimum amount of sodium hydroxide or sodium meta silicateto be injected in order to achieve the maximum reduction in the amountof surfactant which will be subsequently adsorbed on the formation. Ifthe subterranean petroleum containing formation matrix is a relativelyclean, i.e., non-clay containing, sand or sandstone, the lower limits ofthe range given above may be used, whereas formations containingrelatively larger amounts of clay may require substantially greaterquantities of the sacrificial inorganic material to achieve the desiredbenefits.

The surfactant may be injected immediately following the injection ofthe aqueous slug of sacrificial inorganic material or it may bedesirable in the instance of using certain surfactants to separate thepreflush slug of soluble strongly basic compound having an oxygencontaining anion from the surfactant slug by the injec- 'tion of aninert fluid. It is usually most convenient to inject an aqueous solutionof surfactant, and it may be desirable to include the sacrificialinorganic material in the surfactant solution, in a concentrationapproximately equal to the concentration of the orginally injectedpreflush slug. injection of the surfactant solution may be continued aslong as is desired, although economicsgenerally dictate that suchinjection be terminated and that a more economical fluid such as waterbe injected thereafter to displace the surfactant slug and displaced oilthrough the reservoir.

Pre-treating the subterranean petroleum containing reservoir with watersoluble, strongly basic materials having an oxygen containing anion isespecially effective in reducing adsorptionof non-ionic surfactants.Accordingly, an especially preferred embodiment of this inventioninvolves injecting an aqueous slug of these sacrificial inorganicmaterials followed by the injection of an aqueous solution of anon-ionic surfactant into the said formation, followed by injection ofwater.

-While this invention has been described primarily as an improved methodof conducting a surfactant-water flooding oil recovery program, itshould be recognized that the same sacrificial inorganic materials arevery effective for inhibiting the adsorption of polymeric materialsincorporated into the injection fluid for the purpose of increasing theviscosity of said fluid. For example, the aqueous solution of sodiumhydroxide or so dium meta silicate may be used to pretreat a formation,followed by the injection of an aqueous solution of viscosity increasingpolymer such as polyacrylami dg Since the pre-treatment with thisiri'o'ig a nic sacrificial material inhibits the adsorption fromsolution of the polyacrylamide, the viscosity of the injected fluid willremain more constant throughout the displacement process. The totaleffectiveness of the viscous flood will be improved by use of thepreflush of sacrificial inorganic material.

The effectiveness of this invention for reducing the adsorption ofsurfactant on formation rock in surfactant water flooding operations isdemonstrated by the following examples, which are presented by way ofillustration and are not intended as limiting the spirit and scope ofthe invention as are defined hereinafter in the claims.

In order to test the adsorption of a non-ionic surfactant on sand, acolumn was filled with sieved 150-200 mesh silica sand which had beenthoroughly washed to remove all fines. A weighted quantity of this sandwas added to the column and the port volume of the column wasdetermined. if a preflush solution was to be tested to determine theextent that it could decrease the adsorption of the surfactant, 100 ml.of a known concentration of this additive was passed through the columnand followed by 25 milliliters of a known concentration of thesurfactant previously described. Distilled water was passediifiifigifine column and samples of the effluent from the column weretaken at intervals. Concentrations of surfactant were measured byspectrophotometry. In Table I, data are given indicating the extent ofadsorption of the surfactant on the sand when no preflush was used inRun 1 and when the sand was pretreated with an aqueous solution of 1.0molar (4 percent by weight) sodium hydroxide in Run 2, and with a 1.0molar (12 percent by weight) solution of sodium meta silicate in Run 3.Column 11 gives the pore volumes of water which were flowed through thesand to elute 60 percent of the surfactant. Column 111 gives the porevolumes of water which were passed through the column to elute percentof th surfactant. Column lV gives the port volumes of water which werepassed through the column in order to elute 90 percent of the surfactantafter the surfactant first appeared in the effluent. Those instances inwhich a larger quantity of the surfactant were adsorbed on the sand areindicated by the necessity of passing greater quantities of waterthrough the sand in order to elute a given amount of the surfactant.

Line 4 of Table 1 gives values calculated as the theoretical potentialvalue, based on surfactant spreading and assuming that no adsorptionoccurred on a column of sand identical to that used in the experiment.Line 5 of Table I gives the results obtained on an identical column ofsand using a sample of potassium permanganate on a column which had beendeactivated by saturating with potassium permanganate to eliminatespreading due to adsorption. Runs 4 and 5 present the best possibleresults which could be obtained by using any preflush treatment. It canbe seen from these data that both sodium hydroxide and sodium metasilicate are extremely effective at reducing the adsorption ofsurfactant on the sand particle surfaces.

1 ll 111 IV Pore volumes of water to elute 90% Pore volumes Pore volumesof water of water of surfactant to elute 60% to elute 90% after firstPreflush of surfactant of surfactant appearance of surfactant 1. None4.90 8.43 6. 2. 1.0 molar Sodium Hydroxide 2.34 4.55 3.05 3. 1.0 molarSodium Meta Silicate 1.89 3 .94 2.44 4. Theoretical Calculations 1.361.67 0.96 5. 26 ppm. Potassium Permanganate 1.42 1.75 0.97

It will be appreciated by those skilled in the art that since it is theoxygen containing anion that is adsorbed by the formation, the cationpresent in the compound has no appreciable affect on the operability ofthe compound. That is, any other soluble hydroxide such as potassiumhydroxide will function in essentially the same manner as sodiumhydroxide. Similarly, potassium silicate is as effective for use as apreflush in accordance with this invention as sodium meta silicate.Further, any of the soluble compounds containing both silicon and oxygenin the anion, such as sodium silicate or sodium ortho silicate, willfunction in essentially the same manner as sodium meta silicate.

Thus it can be seen that by injecting into a subterranean formation asmall quantity of a water soluble, strongly basic material having anoxygen containing anion such as sodium hydroxide or sodium metasilicate, the amount of subsequently injected surfactant which isadsorbed onto the formation can be dramatically decreased. Since lesssurfactant is required for a flood, supplemental recovery techniques canbe performed with improved economics. By preventing the adsorption ofsurfactant by the formation, the concentration of surfactant may bemaintained relatively constant throughout the progress of thesupplemental recovery technique, whereby the oil recovery efficiency isimproved.

Various embodiments and modifications of this invention are apparentfrom the foregoing description and examples, and further modificationswill be apparent to those skilled in the art. These modifications areincluded within the scope of this invention as defined by the claimsbelow.

We claim: 1. In a method of recovering oil from a subterranean petroleumcontaining formation wherein an aqueous flooding medium containing asurfactant adsorbable by the formation rock is injected throughinjection means, the improvement which comprises injecting watersoluble, strongly basic compounds having an oxygenated anion in at leastan amount sufficient to satisfy substantially all of the adsorptioncapacity of the formation rock into said formation prior to theinjection of said surfactant.

2. The method of claim 1 wherein the water soluble strongly basiccompound is selected from the group consisting of sodium hydroxide andsodium silicates.

3. The method of claim 1 wherein the water soluble strong basic compoundis sodium hydroxide.

4. The method of claim 1 wherein the water soluble strongly basiccompound is sodium meta silicate.

5. The method of claim 1 wherein the water soluble, strongly basiccompound having an oxygenated anion is injected in aqueous solution.

6. The method of claim 1 wherein the water soluble strongly basiccompound having an oxygenated anion is in an aqueous solution of fromabout 0.1 to about 2.0 molar sodium hydroxide.

7. The method of claim 6 wherein from about 0.005 to about 0.1 porevolumes of said aqueous sodium hydroxide solution is injected into thereservoir.

8. The method of claim 1 wherein the water soluble strongly basiccompound having an oxygenated anion is injected as an aqueous solutionof from about 0.1 to about 2.0 molar sodium meta silicate.

9. The method of claim 8 wherein from about 0.005 to about 0.1 porevolumes of said aqueous sodium meta silicate solution is injected intothe reservoir.

10. The method of claim 1 wherein from about 50 to about 500 pounds ofsaid water soluble strongly basic compound per acre foot of formation tobe swept is injected into the formation.

11. The method of claim 1 wherein from about 50 to about 500 pounds ofsodium hydroxide per acre foot of formation to be swept is injected intothe formation.

12. The method of claim 1 wherein from about 50 to about 1,000 pounds ofsodium meta silicate per acre foot of formation to be swept is injectedinto the formation.

13. The method of claim 1 wherein the water soluble strongly basiccompound having an oxygenated anion is injected in aqueous solutionwhich also contains sodium chloride.

14. The method of claim 1 wherein the surfactant is injected as anaqueous solution which also contains sodium chloride.

15. The method of claim 1 wherein the surfactant is injected as anaqueous solution which additionally contains the water soluble, stronglybasic compound having an oxygenated anion used in the preflush.

mg UNITED STATES PATENT OFFICE I i CERTIFICATE OF CORRECTION Patent No.3,777,817 1 Dated December 11 1973 Inventor(s )David George Feuerbecher,Mary Kay Hrncir Smith It is certified that error appears in theabove-identified patent and that said Letters Patent are herebycorrected as shown below:

' Column 2, line 9, "the" should be --frequently--.'

Column 2, line 18, "fliud" should be ---iEluid---. I

Column 2, line 19, "is" should be ---in--. 1 Column 2, line 21, h"should be "the".

Column 3, line 38, 'appreclebel" should be "appreciable". Column 3, line41, "with" should be --wh1eh---.

Column 3, line 68, "aqueous" should be aqueous- Column n, line 10,"injected" should be "injection". Column l line 53, "program" should be--progre.m-.

Column 6, line 45, "th" should be the-w.

Column 6, line 62, "present" should be "represent"; 001m 7, line 9 under0011mm I, e "to elute 60%" should be moved from Column I to Column II.(The heading of Column I should read --Preflush-- and the heading ofColumn II should read --Pore Volumes of Water to E t 0f Surfactant, v

signe and sealed this 24th day of September 1974.

(SEAL) Attest:

McCOY M. GIBSON JR. c. MARSHALL DANN Attesting Officer Commissioner ofPatents

2. The method of claim 1 wherein the water soluble strongly basic compound is selected from the group consisting of sodium hydroxide and sodium silicates.
 3. The method of claim 1 wherein the water soluble strong basic compound is sodium hydroxide.
 4. The method of claim 1 wherein the water soluble strongly basic compound is sodium meta silicate.
 5. The method of claim 1 wherein the water soluble, strongly basic compound having an oxygenated anion is injected in aqueous solution.
 6. The method of claim 1 wherein the water soluble strongly basic compound having an oxygenated anion is in an aqueous solution of from about 0.1 to about 2.0 molar sodium hydroxide.
 7. The method of claim 6 wherein from about 0.005 to about 0.1 pore volumes of said aqueous sodium hydroxide solution is injected into the reservoir.
 8. The method of claim 1 wherein the water soluble strongly basic compound having an oxygenated anion is injected as an aqueous solution of from about 0.1 to about 2.0 molar sodium meta silicate.
 9. The method of claim 8 wherein from about 0.005 to about 0.1 pore volumes of said aqueous sodium meta silicate solution is injected into the reservoir.
 10. The method of claim 1 wherein from about 50 to about 500 pounds of said water soluble strongly basic compound per acre foot of formation to be swept is injected into the formation.
 11. The method of claim 1 wherein from about 50 to about 500 pounds of sodium hydroxide per acre foot of formation to be swept is injected into the formation.
 12. The method of claim 1 wherein from about 50 to about 1,000 pounds of sodium meta silicate per acre foot of formation to be swept is injected into the formation.
 13. The method of claim 1 wherein the water soluble strongly basic compound having an oxygenated anion is injected in aqueous solution which also contains sodium chloride.
 14. The method of claim 1 wherein the surfactant is injected as an aqueous solution which also contains sodium chloride.
 15. The method of claim 1 wherein the surfactant is injected as an aqueous solution which additionally contains the water soluble, strongly basic compound having an oxygenated anion used in the preflush. 